This invention relates to jacketed polymer optical waveguides, more particularly, polymer optical waveguides jacketed with chlorinated polyethylene or compositions containing chlorinated polyethylene.
Polymer optical waveguides comprise a light-transmitting, polymeric core material and a cladding around the core formed from a second polymer having a lower refractive index than that of the core material, said cladding being designed to prevent the light waves from exiting the waveguide by bouncing the light waves back toward the center of the waveguide core.
Polymer optical waveguides are used to transmit light for various functions. The waveguides may be used as part of a sensor for a particular phenomena or material. Alternatively, the polymer optical waveguides may be used to transmit information by discrete light pulses. In some embodiments the polymer optical waveguides are used as cables connecting various information transmitting and receiving machines, for example, computers, telephones, and the like. It is desirable to protect the polymer optical waveguides from certain environments to which the waveguides are exposed. One way to do such is to jacket the polymer optical waveguides. Polymer optical waveguides may be jacketed with a variety of polymeric jacketing materials. Examples of suitable jacketing materials include natural and synthetic rubbers and alpha-mono-olefin polymers and copolymers, such as polyethylene, preferably having low or medium density, polypropylene, and vinyl chloride polymers and co-polymers each containing non-migratory plasticizers.
There are two general types of jacketing processes, pressure type extrusion process and tubing type extrusion process. The most serious problem in jacketing polymer optical waveguides is that many presently available materials used in polymer optical waveguides are heat sensitive at temperatures as low as 80.degree. C. In some extrusion jacketing processes, the extrudable jacketing material is at a temperature well in excess of 130.degree. C. within the extruder. Thus, the jacketing material must not be allowed to remain in prolonged contact with the polymer optical waveguides within the extruder or substantial degradation of the polymer optical waveguide, or its optical transmission properties may occur. In a pressure type extrusion process, the polymer optical waveguide may be subjected to high temperatures and pressures for a sufficient period of time to cause such degradation. In addition, the pressure type extrusion process cannot be used to jacket a multi-strand bundle of filamentary material because the bundle is not round and would fail to seal the outlet of the filament guide within the extruder. The seal failure results in leakage of the extrudable material back into the filament guide.
In a tubing type extrusion process, the major problem faced is that on extrusion of the plastic tube the inner diameter of the plastic tube is larger than the outer diameter of the filamentary material which results in a loose fit. It is important that the filaments be held firmly at each end of the light guide for efficient pick up and display of light. Light guides prepared using a loose jacket require the ends to be specially treated by potting or clamping to immobilize ends. This problem can be partially solved by stretching the tubing while it is being drawn down around the filamentary material, but this creates stresses in the tubing which cannot be relieved on a production line basis due to the low heat tolerance of plastic optical waveguides. Due to these stresses, the tubing or jacket may later shrink when subjected to in-service temperatures thereby leaving the polymer optical waveguide exposed and possibly yielding a kinked waveguide.
Materials described as useful for jacketing polymer optical waveguides are alpha-mono-olefins, for example, polyethylene and polypropylene. See U.S. Pat. No. 3,646,186 (relevant portions incorporated herein). Polyethylene has a relatively low use temperature, however, and may not be suitable for use in polymer optical waveguides which will be exposed to somewhat higher temperatures in service. Other materials, which U.S. Pat. No. 3,646,186 indicates are useful for jacketing of polymer optical waveguides, are the vinyl chloride polymers and co-polymers, for example, polyvinyl chloride. Polyvinyl chloride alone can be very brittle; therefore, plasticizers are required to reduce the brittleness of polyvinyl chloride. Most known plasticizers for polyvinyl chloride are migratory and may migrate into the cladding of the polymer optical waveguide changing the refractive index and therefore, the light transmission properties of the optical waveguide. Non-migratory plasticizers may be used, but such plasticizers are relatively expensive. In addition, polyvinyl chloride has relatively poor solvent resistance. Furthermore, such polymers often lack the rigidity which is desirable for jackets for polymer optical waveguides.
What is needed is a polymer optical waveguide with a jacketing which has a higher use temperature than polyethylene, or a use temperature which matches or exceeds that of the optical waveguide. What is further needed is a polymer optical waveguide with a jacketing material which can be formed about the polymer optical waveguide at temperatures which do not significantly damage or degrade the polymer optical waveguide. What is further desired is a polymer optical waveguide which is jacketed with a material which has good rigidity, low brittleness at use temperatures, and good solvent resistance. What is further needed is a polymer optical waveguide which is jacketed with a material which does not contain additives which will migrate into the polymer optical waveguide and substantially change the optical properties of said polymer optical waveguide.